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Flashcards in Cytoskeleton II Deck (28):

Cyto skeleton motor dependent types

Motor driven or polymerization-driven

Intracellular transport-motor-driven or polymerization-driven

Ciliar/flagellar beating


What makes up contractile ring/what is its function

Actin and myosin filaments

Used to cleave the cell in two


How does city skeleton drive morphogenesis

Invagination of epithelial sheet is caused by organized tightening of adhesion belts
-associated with actin filaments/myosin II


Traffic direction

Both ways on actin and MT


3 classes of cytoskeletal motors

Myosins-move along actin filaments

Dyneins/kinesins-move along Mts
(dynein is much bigger)

All three classes are ATP ases and have multiple isomforms encoded by multiple ones


Molecular motor facts (5)

All atpases

Related structure and mechs-large gene families

Partiulular isoform moves in one direction

Vesiceles/organelles move on microtubules and actin filaments + more than one kind of motor

Downstream targets of cellular signalling cascades


Molecular motor energetics

Energy from ATP hydrolysis-causes conformational change
-tension or moments is generated along filament or MT


Myosin facts

Large gene family

Two heavy chains, tw or more light chains

Most move toward plus direction

Globular head with Atlases

Tail is variable domain-coiled coil for dimerization and/or binds to membrane or target vesicle

Classification based on motor domain

Mutations-result in inherited human diseases


Kinesin facts

Motor domain (head)-heavy chains contain ATPase and MT binding site
-N terminal is plus end directed
-C terminal is minus end directed

Kinesin 1C is bound to tail

Neckregion determines opolarity
Stalk is coiled for dimerization

Tail binds to varaible target and to light chains


Dyenin facts

Minus end directed


AAA proteins (ATPase associated with diverse cellular activities)
-energy from hydrolysis, conformationatal change, work

In cilia/flagella

From periphery of cell to nucleus

Can see in EM as little spur

When has ATP bounds attached to microtubule
-lose P and released


Karatagener syndrome

Primary ciliary dyskinesia

Resp tract infections/male infertility

Mislocalized dyenin-stuck in basal body

Cilia are immotile-mutation is in outer arm ciliary dyne heavy chain, outer arms mmissing


How do cytoskeletal motors work

ATP energy to mechanical work and heat
-conformational change

rate limiting step is Phosphate release following hydrolysis
-binding to actin or microtubules accelerates rate limiting step
-actin/MT is nucleotide exchange factor

Kinesin and myosin differ in processivity


Myosin II firing

Add ATP- conformational change and release, before hydrolysis
-add ATP-release from actin
-recovery stroke occurs

Release ATp-rebind-actin speeds up, power stroke-rigor mortis--stuck on-actin


What determines myosin speed

rate of myosin ATPase


How reg function of myosin

OM (drug)-binds to cardiac myosin, increases contractility bu accelerating Phospaht erelease-accelerating transition to strong bind and icnreaesd force


Kinesin firing

Bind of ATP weakens affinity for MT

P lease-binds with higher affinity

MT binding accelerates product release and conversion from weak to strong binding (power stroke)


Power stroke

Conversion of weak to strong binding


Kinesan walking

Trai]ling head has ADP and weakly associates wit hMT

ATP head bond to MT

They switch when ATP is hydrolyzed and adde


Motor, substrate track and direction of movement

Myo-ATP-actin-Plus end (mostly)

Kinesan-ATP-MT-Plus end (mostly)

Dyenin-ATP-MT-Minus end


Localization of motors

Tail determins localization
-bind to specific targets

head determines classifcatio/identity/motor function

Antibodies also allow localization of myosin and kinesin isoforms


What is between motor and cargo

Sometimes many proteins that allow great increase of specificity and regulation
-scaffoleer, adaptor, direct bind etc.



Multifunctional protein complex that increases precocity of dyenin-helps bind to MT and other proteins

Binds to tail of dyeing

Has many parters including spectrin that help binding


Which way does traffic go on MT's and actin

Both ways-can be short or long


Intracellular transport facts

many things are transported from ER to cell periphery and back

Transport can occur on _ end of MT as MT grows

Vesicles/organleles can have more than one molecular motor=can travel on both MT and actin


Transport of pigment granulaes

Pigment is in melanosome vesiceles
(melanocytes-cells that make pigment)

Redistribution requires transport on MT and actin filaments

Melanocytes are from neural crest cells

Myosin 5-if don't have won't have normal pigmentation


Myosin V

Binds to carbgo via melanophilin and RabGTPs

Need entire thing to move melaosomes

Myosin 5 attaches from actin to the melanosome


Ras GTPases

target myosin to specific intracellular membranes

if defeiceint-cant target to specific area-cluster in areas where they shouldn't be


Griscelli type 1

elejalde syndrome

Silvery hair, light skin in child of dark skinned parents

neuro defects

Bigpment clumped in hair and not distributed as in normal hair

Malosomes stunch in basal ep-not anywhere else